This invention relates to commutator assemblies for dynamoelectric machines of the type in which a metallic brush contacts commutator bars made of a composite carbon material. Such an arrangement of metallic brushes and carbon commutator bars has a number of advantages over the usual arrangement of metallic commutator bars and carbon brushes. The softer carbon composite material of the commutator bars increases slot tooling life and decreases the number of burrs created on the edge of the commutator bars. In addition, a narrower slot may be possible to help reduce commutator noise. A metallic brush in the form of a leaf spring reduces the mass and number of parts in the brush system for reduced noise and greater ease of assembly. With proper brush-spring pressure optimization, the possibility of reduced brush bounce with resultant reduced arcing and radio frequency interference is present. The simplicity of the arrangement may also allow size and weight reduction in the dynamoelectric machine.
However, this arrangement has its own problems which have prevented it from being utilized in any great volume. One of these problems is the migration of the commutator bars under the pressure of the spring during rotational operation. Since the composite carbon bars are separated and formed by axial slots cut through an annulus of carbon composite material mounted on a cylindrical core, the only anchoring of the bars on the core shown in the prior art has generally been the adhesive and/or friction between the core and the surface of each bar. This has often proven inadequate to positively maintain the commutator bars in their correct positions under the force of the metallic springs during rotational operation of the commutator apparatus.